The present invention generally relates to transmission of optical signals over a multi-channel fiber optic cable, and more particularly, to a method for skewing or deskewing the channels in an optic fiber cable.
It is a common problem in the industry of fiber optic data transmission that the optic pulse transit time in parallel optical links or channels can vary to such a degree that overall system performance is degraded through pulse arrival time mismatch. While ribbon cables can be produced that have low channel-to-channel skew, this manual matching of individual optic channel skew rates is only capable of producing multi-channel cables having one to two picoseconds/meter skew values over relatively short cable lengths, typically in the range of 1 to 15 meters. This optical skew has been addressed in the past by allowing sufficient time between the optical pulses such that the channel-to-channel skew does not cause simultaneously launched optical pulses in different optical channels to arrive at such temporally displaced increments that the following pulse on the fastest channel arrives prior to the initial pulse on the slowest channel. It has been known to correct the skew in an ooptical channel electronically or through the addition active deskew devices, which has previously been done in short length optical cables, such as in high performance computer systems.
Based on the increased need for high speed transmission, there is a desire in the industry to have optical channel lengths of 100 meters or greater having optical skews less than 100 to 200 picoseconds based on the prior known methodology.
Briefly stated, the present invention provides a method to skew or deskew a plurality of optical channels in a multichannel optical cable. The method includes the steps of determining an optical pulse transmission time in at least a first channel and a second channel of the multichannel optical cable. A relative pulse delay between the at least first and the second channels of the multi-channel optical cable is calculated. Delay optics with the appropriate relative pulse delay are serially optically connected to at least one of the channels to one of skew or deskew the first channel relative to the second channel.
In a preferred method, the optical pulse transmission time in each of the channels of the multi-channel optical cable is determined. The relative pulse delay between each of the channels relative to a slowest channel is calculated and mapped. Delay optical waveguides with the appropriate delay time are serially optically connected to each of the respective channels, except the slowest channel, to deskew each of the channels relative to one another.